Apparatus, system, and method for sharing output contacts across multiple relays

ABSTRACT

A power system device-to-device direct communication system comprises a first intelligent electronic device with a processor and a transmit module. Software within the processor maintains a list of “virtual outputs,” which correspond to a number of data channels maintained within the transmit module. The second intelligent electronic device receives the data channels from the first intelligent electronic device and extracts the virtual output bits. The second intelligent electronic device then adjusts a group of its own output contacts in accordance with the received virtual output bits.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/211,816, filed Aug. 25, 2005 now U.S. Pat. No. 7,463,467,which is itself a continuation-in-part of U.S. patent application Ser.No. 09/900,098, filed Jul. 6, 2001, and now U.S. Pat. No. 6,947,269.

FIELD OF THE INVENTION

The present invention relates generally to apparatus, systems, andmethods for sharing resources across power protection devices, and moreparticularly to apparatus, systems, and methods for sharing contacts andforwarding commands across power protection devices using directdevice-to-device communications, and even more particularly toapparatus, systems, and methods for sharing contacts and forwardingcommands across identical power protection devices configured as aprimary and a backup device.

DESCRIPTION OF THE PRIOR ART

In U.S. Pat. No. 5,793,750, the contents of which are herebyincorporated by reference, a communication system between twomicroprocessor-based protective relays for an electric power system isdisclosed. Each of the two relays in that system has both transmit andreceive modules, for directly transmitting indication status bitsindicative of the result of selected protective functions of one relayfrom that one relay to the other, and vice versa.

The output status indication bits are sometimes used to identify theexistence and location of a fault on the power line portion served bythe two relays. One or both of the relays might initiate a circuitbreaker trip action on the basis of the exchange of such information.The output status indication bits may be the result of processingfunctions in one of the relays involving the voltages and/or currents onthe power line monitored by that relay. The output status indicationbits may be used for various control, status, indication and protectionfunctions. Examples of protection functions include permissiveoverreaching transfer trip (POTT) actions, permissive under-reachingtransfer trip (PUTT) actions, directional comparison unblocking (DCUB)and direct transfer trip (DTT) actions. Other relay-to-relay operationsare possible using particular output status indication bits.

The advantage of the communication system described in the '750application is that it is fast and secure. Protective relays typicallyaccomplish their monitoring functions several times each power systemcycle. The '750 communication system provides the results of thesemonitoring functions of one relay, to the other relay. The informationis transmitted directly over a communications link from an originatingrelay which may or may not trip its associated circuit breaker based onits operational results, to another relay. The receiving relay then usesthe transmitted information, in the form of digital bits, to perform itsown on-going calculations, producing various protection actions such astripping and closing a circuit breaker when appropriate. Thecommunication between the two relays may be bidirectional, allowing thetwo relays to exchange information concerning the results of their owncalculations both quickly and securely, with a minimum amount ofexpense.

Power protection devices, such as power protection relays, are ofteninstalled in a primary-backup configuration. The two devices maintainconstant communication, with the primary device sending a health signalto the backup device. The backup device assumes the protection functionif the health signal drops beneath a certain level or disappearsentirely. This adds a level of reliability to the protected powersystem.

Power protection devices must interface with an operator's powerprotection site, and therefore, must gather information from otherequipment at the site and provide certain information to other equipmentat the site. Power protection devices may accomplish this in a varietyof ways, such as through the use of a network. However, input and outputcontacts are the most common way to exchange information between powerprotection devices. For instance, power protection devices frequentlymust know the status of the contacts of a circuit breaker or recloser,before ordering the circuit breaker or recloser to open or close. Thisis provided as a contact input to an interested power protection device.Further, operators often maintain alarm grids, from which they canmonitor the operation of their networks. When a power protection devicedetects a fault, and orders an associated breaker or recloser to trip,the power protection device closes an output contact attached to theoperator's alarm grid.

Often, inputs and outputs can be divided into critical and non-criticalfunctions. For instance, an alarm status output related to gas pressurein a monitored circuit breaker would not be judged as critical, while anovercurrent condition resulting in the relay tripping a circuit breakerwould be judged as critical. When power protection devices areconfigured as primary and backup, operators may specify differentoutputs and inputs for each device, with critical functions handled bythe primary device or redundantly.

When possible, power protection device suppliers and system operatorsprefer to use the same device for both the primary and backup protectiondevice. However, operator specifications may make it difficult orimpossible for a supplier to fill a contract with only one device,particularly in regards to input and output contact requirements for theseparate devices, as well as space requirements. For instance, anoperator specification may require that both the primary and secondarydevices fit in a single rack, and that neither device is more than fourrack units in height. Further, the operator may require the primarydevice to provide fourteen contact outputs and twenty contact inputs,and the backup device to provide no contact inputs and four contactoutputs. Notwithstanding that a total of eighteen contact outputs andtwenty contact inputs are required, if the provider wished to utilizethe same equipment as both the primary and the backup using presenttechnology, the provider would have to provide two devices with fourteencontact outputs and twenty contact inputs. This would leave ten contactoutputs and twenty contact inputs unused on the backup device, whichwould be inefficient. Further, a device with fourteen contact outputsand twenty contact inputs may be larger than a four unit high rackdevice.

One reference in the prior art touches on this issue, although it doesnot directly address it. U.S. Pat. No. 7,027,896, filed Aug. 19, 2003,and issued to Michael Thomson of Schweitzer Engineering Laboratories ofPullman Wash., discloses a substation control system utilizing a numberof input/output modules used to gather inputs from a power substationfor a number of logic processors, which communicate with theinput/output modules through a fiber-optic network. However, thisreference does not disclose resource sharing or command forwardingbetween intelligent power protection devices.

OBJECTS OF THE INVENTION

Accordingly, it is an object of this invention to provide a mechanism toshare output contacts across multiple power protection devices.

Another object of this invention is to provide a communications protocolbetween multiple power protection devices for sharing contacts.

Yet another object of this invention is to provide a communicationsprotocol whereby one power protection device can forward commands toanother power protection device.

SUMMARY OF THE INVENTION

The disclosed invention achieves its objectives through the use of adevice-to-device direct communication system. The device-to-devicedirect communication system allows one device to utilize both the inputand output contacts of the other device as needed. In addition, onedevice may forward or source commands to the other device.

In one embodiment of the invention, a power system device-to-devicedirect communication system comprises a first intelligent electronicdevice with a processor and a transmit module. Software within theprocessor maintains a list of “virtual outputs.” Within the transmitmodule, part of which may be implemented within the processor, a numberof data channels are maintained. The processor transfers the virtualoutputs into the data channels, and transmits the data channels to asecond intelligent electronic device. The second intelligent electronicdevice receives the data channels and extracts the virtual output bits.The second intelligent electronic device then adjusts a group of its ownoutput contacts in accordance with the received virtual output bits.

In another embodiment of the invention, a power system device-to-devicedirect communication system comprises a first intelligent electronicdevice with a first processor and a receive module coupled to acommunication link. The receive module receives channel data from thecommunication link including a virtual input. The processor examines thereceived data including the virtual input and alters its internal statebased on the received data. A second intelligent electronic devicemonitors its input contact with a second processor. The secondintelligent electronic device also has a transmit module coupled to thesecond processor, where a plurality of data channels are formedincluding a virtual input formed from the status of the input, which istransmitted to the first intelligent electronic device.

In a further embodiment of the invention, a power systemdevice-to-device communication system comprises a first intelligentelectronic device with a first processor, a command input, and atransmit module coupled to a communication link. The first processorforms a plurality of data channels including at least one commandchannel based on the command input, and transmits the plurality of datachannels to a second intelligent electronic device. The secondintelligent electronic device receives the plurality of data channelswith a receive module and extracts the command channels using a secondprocessor. The second processor then executes the command.

BRIEF DESCRIPTION OF THE DRAWINGS

Although the characteristic features of this invention will beparticularly pointed out in the claims, the invention itself, and themanner in which it can be made and used, can be better understood byreferring to the following description taken in connection with theaccompanying drawings forming a part hereof, wherein like referencenumerals refer to like parts throughout the several views and in which:

FIG. 1 is a simplified single line schematic diagram of a typical widearea power system.

FIG. 2 is a simplified block diagram of a relay-to-relay directcommunication system within the power system of FIG. 1 constructed inaccordance with an embodiment of the invention.

FIG. 3 is an exemplary-received frame of the relay-to-relay directcommunication system of FIG. 2.

FIG. 4 is a simplified functional block diagram of a system constructedin accordance with the an embodiment of the invention wherein a primarypower protection device controls the functioning of a backup powerprotection device.

FIG. 5 is a simplified block diagram of a relay-to-relay directcommunication system for use in the power system of FIG. 1, constructedin accordance with an embodiment of the invention.

FIG. 6 is an exemplary-received frame of the relay-to-relay directcommunication system of FIG. 4.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

As indicated above, the present invention is based on and is animprovement of the communication system of U.S. Pat. No. 5,793,750,which includes a direct communication link between two protective relaysserving an electric power apparatus, the system supporting acommunication arrangement or protocol involving eight data channels forexchange of output status indication bits between the two relays bothquickly and securely. The channel data bits TMB1-TMB8 identify eighttransmit bits, on eight data channels.

Those bits, when received by the other relay, are identified as receivedchannel data bits RMB1-RMB8, wherein RMB1-RMB8 are the “mirror” orreplica of the transmit channel data bits. The eight data channels canaccommodate at least eight output status indication bits. As indicatedabove, however, in many two-relay arrangements, only two or perhapsthree channels are necessary to communicate the output status indicationbits. Utilizing the present invention, the otherwise vacant channelspace can now be used by selected additional data (discussed below) andan associated synchronization channel to synchronize the additionaldata.

The additional data can be digitized analog quantities, such as meteringdata, or can be “virtual terminal” data. In a virtual terminalimplementation, a human user or another application utilizes the directcommunication link to communicate with the other relay. For example, thehuman user could utilize the direct communications link to control orquery the other relay. An application such as, for example, anintegration protocol like as DNP3, could also utilize the communicationslink in the virtual terminal implementation.

FIG. 1 is a simplified single line schematic diagram of a typical widearea power system 10. As illustrated in FIG. 1, the power system 10includes, among other things, two generators 12 each configured togenerate three-phase sinusoidal waveforms, for example, three-phase 12kV sinusoidal waveforms, two step-up power transformers 14 configured toincrease the 12 kV sinusoidal waveforms to a higher voltage, such as 138kV, and a number of circuit breakers 18. The step-up power transformers14 provide the higher voltage sinusoidal waveforms to a number of longdistance transmission lines such as the transmission lines 20. In oneembodiment, a first substation 16 may be defined to include thegenerators 12, the step-up transformers 14 and the circuit breakers 18,all interconnected via a first bus 19. At the end of the long distancetransmission lines 20, a second substation 22 may include step-downpower transformers 24 to transform the higher voltage sinusoidalwaveforms to lower voltage sinusoidal waveforms (e.g., 15 kV) suitablefor distribution via a distribution line to various end users 26 andloads 30.

As previously mentioned, the power system 10 includes protective devicesand procedures to protect the power system elements from faults or otherabnormal conditions The protective devices and procedures utilize avariety of protective logic schemes to determine whether a fault orother problem exists in the power system. For example, some types ofprotective relays utilize a current differential comparison to determinewhether a fault exists in the protection zone. Other types of protectiverelays compare the magnitudes of calculated phasors, representative ofthe power system sinusoidal waveforms, to determine whether a faultexists in the protection zone. Frequency sensing techniques and harmoniccontent detection is also incorporated in protective relays to detectfault conditions. Similarly, thermal model schemes are utilized byprotective relays to determine whether a thermal problem exists in theprotection zone.

Referring again to FIG. 1, also included are a first and a secondprotective relay 100 and 102 adapted to provide for example, overcurrentprotection for the transmission line 21. As described below, the firstand second protective relays 100, 102 are also adapted to communicatevia a communication link 34 that can be configured using one of a numberof suitable media. Additional protective relays such as a protectiverelay 104, adapted to communicate with the first protective relay 100and/or the second protective relay 102, may also be included in thepower system 10.

FIG. 2 is a simplified block diagram of a relay-to-relay directcommunication system 40 incorporated in the power system 10. Althoughillustrated using the first and second protective relays 100, 102, itshould be understood that the communication system 40 can includeadditional protective relays operatively coupled to the first and/orsecond relay 100, 102 and adapted to operate as described below.Further, although illustrated using the first and second protectiverelays 100, 102, it should be understood that the apparatus and methoddescribed herein is applicable to communication between any intelligentelectronic device (IED) of the power system 10.

For ease of discussion, the first protective relay 100 is shown as thetransmitting relay and includes, inter alia, a “transmit” module 41,having a microcontroller 42 operatively coupled to a receive andtransmit interface means; in this example, a universal asynchronousreceiver/transmitter (UART) 43. The (transmitting) UART 43 is configuredto convert bytes of channel data bits (corresponding to the channeldata) resulting from operation of the first protective relay 100 into asingle serial message stream for outbound transmission via thecommunication link 34 to the second protective relay 102, and to convertan inbound serial message stream (from the second protective relay 102)into bytes of channel data suitable for use by the first protectiverelay 100.

Similarly, the second protective relay 102 is shown as the receivingrelay and includes, inter alia, a “receive” module 44 having a secondmicrocontroller 45 operatively coupled to another UART 46, operationaland configured as described above. Although not separately illustrated,each of the first and second protective relays 100, 102 include bothtransmit and receive capability to enable communication. Whileillustrated as transmit and receive modules 41, 44, in a simplifiedfunctional block diagram format, the relay-to-relay direct communicationsystem and method described herein may be implemented by means of amicroprocessor or field programmable gate array (FPGA) executing acomputer program, protection algorithm or relay logic scheme. Further,although illustrated as a UART 43 operatively coupled to the firstmicrocontroller 42, and a UART 46 operatively coupled to the secondmicrocontroller 45, one of any suitable transmit and receive interfacemeans may be utilized to convert bytes of channel data bits into aserial message stream for transmission via the communication link 34.

The transmit module 41 and the receive module 44 are operativelyconnected via the communication link 34. As noted above, thecommunication link 34 may be implemented as an RF link, a microwavelink, an audio link, a fiber optic link, or another other type ofsuitable link adapted to carry serial data. As illustrated, in additionto output status indication bits, each of the transmit and receivemodules 41, 44 is capable of transmitting/receiving other types ofchannel data in the form of serial messages. For example, the channeldata may include digitized analog values, derived from analogquantities, that require more than a single bit such as meteringinformation, breaker failure system security enhancement information,reclose enable information, instrument transformer checking andmulti-terminal fault location information, to name a few.

Referring to the transmit module 41, an eight data channel arrangementis configured such that two data channels, a data channel 47 and a datachannel 48, correspond to the conventional output status indication bits57 transmitted as channel data bit TMB1 and TMB2, respectively, from thetransmit module 41 of the first protective relay 100 to the receivemodule 44 of the second protective relay 102. Three data channels, adata channel 49, a data channel 50 and a data channel 51, are dedicatedto digitized analog values 59, 60 and 61 transmitted as channel databits TMB3, TMB4 and TMB5, respectively, from the transmit module 41 ofthe first protective relay 100 to the receive module 44 of the secondprotective relay 102.

Each of the digitized analog values 59, 60, 61 are formed by, forexample, converting a 32-bit floating point number representing ananalog quantity (e.g., system impedances, currents, voltages)) into an18-bit floating point number. The 18-bit floating point number is thenserialized such that one bit from each of the digitized analog values59, 60, 61 is included as channel data bits TMB3, TMB4 and TMB5,respectively, in sequential transmitted messages until all of the bitsassociated with the digitized analog values 59, 60, 61 are transmitted.For example, if each of the digitized analog values 59, 60, 61 isexpressed in 18 bits, eighteen sequential serial messages aretransmitted where the first serial message includes the first bit of thedigitized analog value 59 transmitted as channel data bit TMB3, thefirst bit of the digitized analog value 60 transmitted as channel databit TMB4, and the first bit of the digitized analog value 61 transmittedas channel data bit TMB5. Similarly, the second serial message includesthe second bit of the digitized analog value 59 transmitted as channeldata bit TMB3, the second bit of the digitized analog value 60transmitted as channel data bit TMB4, and the second bit of thedigitized analog value 61 transmitted as channel data bit TMB5, and soon.

It should be noted that while compromising some precision, theconversion scheme that converts a 32-bit floating point number(representing the analog quantity) into a corresponding 18-bit floatingpoint number, enables quicker transmission to the second protectiverelay 102. It should also be noted that other conversion schemes may beutilized depending on the analog quantity measured, the precisionrequired, and the speed of transmission desired.

Two additional data channels, a data channel 52 and a data channel 53facilitate virtual terminal data transmitted as channel data bits TMB6and TMB7, respectively, from the transmit module 41 of the firstprotective relay 100 to the receive module 44 of the second protectiverelay 102. As noted above, virtual terminal data refers to data providedby a user located at a local relay (e.g., the first relay 100), to aremote relay (e.g., the second relay 102) via the communication link 34.In such a configuration, the local relay operates as a virtual terminalto allow the user to query and/or control the remote relay with thefamiliar serial port user interface passing data on otherwise unusedchannels. The virtual terminal scheme also adds fast meter/operatecapability. Like the digitized analog values described above, thevirtual terminal data is serialized bit-by-bit such that, for example,18-bit virtual terminal data is transmitted bit-by-bit in 18 sequentialserial messages where the first two bits are payload flags and the lastsixteen bits are two 8-bit data bytes. For example, the 18-bit virtualterminal data may be expressed as:p.sub.1p.sub.2d.sub.16d.sub.15d.sub.14d.sub.13d-.sub.12d.sub.11d.sub.10d.sub.9d.sub.8d.sub.7d.sub.6d.sub.5d.sub.4d.sub.3d.-sub.1where p.sub.1-1 indicates that d.sub.1-d.sub.8 is a payload byte, andp.sub.2=1 indicates that d.sub.9-d.sub.16 is a payload byte (see, FIG.3).

The eighth data channel 54 is dedicated to synchronization informationtransmitted as channel data bit TMB8 from the transmit module 41 of thefirst protective relay 100 to the receive module 44 of the secondprotective relay 102. The synchronization information enablessynchronization of the data channels associated with the analog values59, 60, 61 and the virtual terminal data 62. Thus, when any of the datachannels 47-53 are used for anything other than the output statusindication bits, a dedicated synchronous channel is allocated forsynchronization information transmitted as channel data bit TMB8.

Although illustrated utilizing an eight data channel arrangement, itshould be understood that a different number or arrangement and/orassignment of data channels can be used by the first and secondprotective relays 100, 102 of the communication system 40. Accordingly,the two data channels of output status indication bits in combinationwith the three data channels of analog values and the two data channelsof virtual terminal data illustrated in FIG. 2 is arbitrary. The outputstatus indication bits could occupy more or less or no data channels,the analog values could occupy more or less or no data channels, and thevirtual terminal data could occupy more or less or no data channels. Inaddition, one analog value can occupy more than one data channel forspeedier transmission. Similarly, virtual terminal data can occupy morethan one data channel for speedier transmission.

Further, in one embodiment of the invention, the arrangement and/orassignment of the data channels may be fixed, while in anotherembodiment, the arrangement and/or assignment of the data channels maybe dynamically changed during relay operation, depending on the desiredconfiguration of the protective relay(s) 100, 102. As a result, speed ofreceipt of the channel data by the receive module 44 is adjustable basedon the assignment of the channel data to the number of data channels.

For example, if 18-bit virtual terminal data is dynamically assigned toone data channel during a high activity period of relay operation, it istransmitted bit-by-bit in 18 sequential serial messages, and thenreassembled for use by the receiving relay. If one message istransmitted every 1 millisecond via the communication link 34, 18milliseconds are required for receipt of the entire 18-bit virtualterminal data. In contrast, if the same 18-bit virtual terminal data isdynamically assigned to three data channels during a lower activityperiod of relay operation, it is transmitted bit-by-bit in 6 sequentialserial messages, requiring six milliseconds.

Prior to transmission, each of the eight channel data bits TMB1-TMB8 isencoded by an encoder 65 to form an encoded message 66 using one of anynumber of suitable techniques. The encoded message 66 may therefore haveone of any number of suitable formats, depending on the encoding schemeselected. For example, in one encoding scheme, the encoded message 66may include 36 or 40 bits, divided into four 9-bit (for 36 bit length)or 10-bit (for 40 bit length) characters plus a number of idle bits. Thenumber of idle bits may vary depending upon the selected transmissionspeed.

Continuing with the example, the bits may be assembled such that thefirst 9-10 bit character includes a single start bit followed by the sixchannel data bits TMB1-TMB6, followed by an odd parity bit and one ortwo stop bits, as selected by the user. The second character may includea second single start bit, followed by the six channel data bits TMB5,TMB6, TMB7, TMB8, TMB1 and TMB2, followed by an odd parity bit and oneor two stop bits. The third character may include a start bit followedby the six channel data bits TMB7, TMB8, TMB1, TMB2, TMB3 and TMB4,followed by an odd parity bit and one or two stop bits. The fourth andfinal character in the message may include a single start bit followedby the six channel data bits TMB3-TMB8, followed by an odd parity bitand one or two stop bits. The remaining bits, if any, are a variablenumber of idle bits, depending upon transmission speed of the data.

Using such an encoding scheme, each of the channel data bits TMB1-TMB8are repeated three times in the four character portions of one encodedmessage 66 with single stop and parity bits and one or two stop bitsinserted between each character portion of the encoded message 66. Thisencoding scheme allows the receiving, or second protective relay 102, tocheck for errors that may have occurred during transmission.

In addition to assembling the bits into messages, each of the first andsecond protective relays 100, 102 may be adapted to further encode anddecode using an identifier pattern selected during system configuration.For example, if preprogrammed to include one particular identifierpattern, the transmit encoder 65 logically inverts one of the fourcharacters in each of the messages as a means of encoding the identifierpattern into the message. As described below, the receiving, or second,relay 102 then ensures that the received message has been encoded withthe correct identifier pattern. Although described as assemblingmessages where one character is logically inverted, it should beunderstood that other suitable formats and encoding schemes may beutilized by the encoder 65 to generate the encoded message 66.

The encoded message 66 is then applied to the UART 43, adapted tosatisfy several operating parameters for the system. In general, theUART 43 converts the encoded message 66 into a serial message 67 fortransmission as part of a serial message stream via the communicationlink 34. Accordingly, the receiving UART 46 must also be capable ofchecking the received serial message 67 for proper framing (the presenceof one stop bit per byte) and proper parity, and detecting overrunerrors.

The UART 43 can be programmed for various baud rates. For example, itcan be programmed for baud rates ranging from 300 through 115,000. TheUART 43 is additionally adapted to synchronize both transmit and receiveserial messages using transmit and receive clocks externally supplied.As will be appreciated by one skilled in the art, the method of bitsynchronization, using start and stop bits or using synchronizingclocks, is one of any number of suitable methods for synchronization.

Subsequent to being prepared for transmission by the UART 43, the serialmessage 67 is transmitted over the communication link 34 to thereceive-module 44. The sampling and transmission rates can be varieddepending on the desired operation of the transmitting relay.

Referring now to the receive module 44, the receiving UART 46 providesthe counterpart functions of the transmitting UART 43. When the serialmessage 67 is received by the receive module 44, the UART 46 performsseveral data checks on each character of the serial message 67. It alsochecks each character of the serial messages 67 for proper framing,parity and overrun errors.

From UART 46, the characters of the serial message 67 are passed to adecoder 68. In general, the decoder 68 reassembles groups of fourcharacters in order to reconstruct the four character message. Next, thedecoder 68 checks each message for errors, and also examines the resultsof the UART checks described above. If any of the checks fail, thedecoder 68 discards the message and de-asserts a DOK (data OK) flag 94for that message in a register 95 (see, FIG. 3).

More specifically, in the illustrated example, the decoder 68 ensuresthat there are the three copies of the eight channel data bits TMB1-TMB8included in the transmitted four-character encoded message 66. If anidentifier pattern was used to encoder the encoded message 66, thedecoder 68 also checks to ensure that the encoded message 66 includesthe identifier pattern. It should be noted that the encoding/decodingscheme described above is one of any number of suitableencoding/decoding schemes to enable error detection that may be utilizedin the method and apparatus of the invention.

As a result of operation of the decoder 68, the DOK flag 94 and thechannel data bits RMB1-RMB8 are provided. The received channel data bitsRMB1-RMB8 are the mirror or replica of transmitted channel data bitsTMB1-TMB8. The data OK (DOK) flag 94 provides an indication of whethererrors were detected in the received message.

Like the transmit module 41 of the first relay 102, the receive module44 of the second relay 102 includes an eight data channel arrangementwhere two data channels are dedicated to the output status indicationbits, three data channels are dedicated to three digitized analogvalues, two data channels are dedicated to virtual terminal data and onedata channel is dedicated to synchronization information. Accordingly,the output status indication bits 57 are received as channel data bitsRMB1 and RMB2 via data channels 70 and 71, respectively, and are appliedto one or more security counters 69. The security counters 69 operate toensure that the state of the received channel data bits RMB1 and RMB2remain constant for a pre-selected number of received serial messages 67before the output status indication bits are utilized by downstreamprocesses. Ensuring that the state of the output status indication bitsremain constant increases the reliability and security associated withthe output status indication bits 57.

Because the two channel data bits RMB1 and RMB2 are transmitted bit bybit, no synchronization of those bits is required. The channel data bitsRMB1 and RMB2 are used by the second relay 102 to make determinationsconcerning operation of the power system 10 (as detected by the firstprotective relay 100) including possible circuit breaker trip actionwhen appropriate. In the illustrated example, the digitized analogvalues 59, 60 and 61 are received as channel data bits RMB3, RMB4, andRMB5 via a data channel 72, a channel 73 and a channel 74, respectively.Each of the three digitized analog values 59, 60, 61 are receivedserially one bit per message per data channel, and are then parallelizedin a parallelize element 78. The parallelize element 78 re-assembleseach of the three digitized analog values from received successivedecoded messages 58. As noted above, in the illustrated example, each ofthe digitized analog values 59, 60, 61 includes eighteen bits. In anembodiment, sixteen bits are used for information while the remainingtwo bits are unused. Therefore, for every 18 messages, a completeoriginal analog value is received on each corresponding data channel.

Similarly, the virtual terminal data 62 is received as channel data bitsRMB6 and RMB7 via data channels 75 and 76, respectively. Like the analogvalues 59, 60, 61, the virtual terminal data 62 is received serially onebit per message per data channel, and is also parallelized in theparallelize element 78. In the illustrated embodiment, the virtualterminal data 62 includes eighteen bits. Sixteen bits of the eighteenbits are utilized for virtual terminal data, where the sixteen bits aredivided into two eight-bit bytes. The two remaining bits are used toindicate which of the two eight-bit byte fields actually contain virtualterminal data, and which, if any, are idle, (e.g., waiting for userinput). Thus, for every 18 decoded messages 58, two virtual terminalbytes are received on each corresponding data channel 75, 76. Afterparallelization via the parallelize element 78, the analog values andthe virtual terminal data are provided to the second protective relay102.

Again, the particular arrangement of the eight data channel bitsTMB1-TMB8 is established in accordance with the user's communicationrequirements. Different numbers of output status indication bits, analogvalues and virtual terminal data can be utilized to form seven bits ofthe eight channel data bits TMB1-TMB8.

A data channel 77, or synchronization channel, is dedicated to theremaining channel data bit, RMB8. The channel data bits RMB8 of thesynchronization channel enable the receiving decoder 68 and parallelizeelement 78 to find the start and stop boundaries serial messages thatinclude the digitized analog values and virtual terminal data. Thesynchronization channel is necessary when any of the other channel databits include the digitized analog values or the virtual terminal data.If all of the channel data bits are used for output status indicationbits only, no synchronization is necessary and the data channel 77 maybe used for output status indication bits.

In order to determine that a complete (four character) bit message hasbeen received, the second relay 102 identifies the first byte of each ofthe bit messages via message synchronization. In one embodiment, messagesynchronization is maintained by counting modulo 4 from the firstreceived byte after byte synchronization is achieved. Accordingly, eachtime the counter rolls over, the first byte is received.

FIG. 3 illustrates an exemplary received frame 80 of the relay-to-relaydirect communication system 40, according to an embodiment of theinvention. As illustrated, the received frame 80 includes 18 messageswhere a series of the “bottom” channel data bit (TMB8) provides the18-bit synchronization information after encoding, transmission anddecoding. In addition, the analog values and virtual terminal data arereceived as channel data bits RMB3-RMB7 via data channels 72-76.

Referring to the data channel 77, or the synchronization channel, aspecial frame synchronization pattern, for example 000001, is utilizedto indicate that all other data channels (e.g., data channels 70-76) areat the beginning of a frame. In the illustrated example, when the lastsix bits received on the synchronization channel are 000001 (the 1 beingmost recent), then the other data channels are determined to be at aframe boundary. For example, the synchronization channel may beexpressed asd.sub.8d.sub.7d.sub.6d.sub.5vd.sub.4d.sub.3d.sub.2d.sub.11pt000001where, d.sub.x=virtual terminal data, 1=binary one, 0=binary zero, p=1indicates that the virtual terminal data is valid, .nu. is a virtualterminal flag byte; it is normally 1, but is set to 0 to indicate aspecial flag byte is in the virtual terminal data, and t=time sync bit.

A comparator 91 in FIG. 3 is adapted to enable detection of the specialframe synchronization pattern in the six most recently received channeldata bits (from the six most recently received messages). Upon detectingthe special frame synchronization pattern via operation of thecomparator 91, a modulo 18 counter 92 is interrogated. If the modulo 18counter 92 is not zero, it is reset to zero and the data on thesynchronization, virtual terminal data and analog value channels (i.e.,channels 72-77) since the last valid frame sync (FS) signal 97 isdiscarded. Therefore, if the modulo 18 counter 92 is at zero, if all ofthe 18 most recent data OK (DOK) flags in register 95 are valid (e.g., abinary 1 value) and if the comparator 91 is asserted indicatingdetection of the special frame synchronization pattern, then an AND-gate96 asserts the FS signal 97, resulting in the analog values and virtualterminal data being utilized by the receiving, or second relay 102.

The synchronization channel, dedicated to the channel data bit RMB8,includes an additional virtual terminal character separated into twofour-bit segments 80 and 82. Further, a bit 84 has a binary 1 value ifthe additional virtual terminal character contains valid data, and hasbinary 0 value if the additional virtual terminal character is idle(such as might be the case if the virtual terminal session is waitingfor input from the user). A bit 85 of the synchronization channel 77 hasa binary 1 value, and a bit 86 typically has a binary 1 value, exceptunder special conditions described below. When both of the bits 84 and85 have a binary 1 value, five consecutive zeros in the synchronizationchannel are not possible. This ensures that the frame synchronizationpattern 000001 detected by comparator 91 can only occur at frameboundaries.

The additional terminal character contained in half-bytes 80 and 82 canalso include control characters, intended to indicate from one relay(transmitting) to the other (receiving) when virtual terminalcommunication should be established, terminated, paused, etc. When oneof these control characters is included in the additional virtualterminal character, bit 86 is forced to a binary 0 value. The specialcontrol characters are chosen carefully by the system designer suchthat, even with bit 86 at the binary 0 value, the frame synchronizationpattern 000001 can only occur at a frame boundary.

In addition, a bit T 98 in the synchronization channel comprises aseparate serial data stream, transmitted at the rate of one bit per 18messages (frame). This separate serial data stream contains date andtime information. Each time the FS signal 97 asserts, a timesynchronization device 88 accepts the bit T 98. An additional framesynchronization system, similar to the frame synchronization systemdescribed above, allows the time synchronization device 88 to recognizethe boundaries between successive time synchronization messages. Namely,a specific frame synchronization pattern is placed in the serial datastream formed by the bit t 98 (i.e., a bit t serial data stream). Acomparator detects the specific frame synchronization pattern, andsignals that the time-of-day and calendar day information, contained inthe bit T serial data stream may be used. The data included in the bit Tserial data stream is formatted such that the frame synchronizationpattern can only occur at frame boundaries. The time synchronizationdevice 88 then updates the time-of-day clock and the calendar day withthe time-of-day and calendar day information contained in the bit Tserial data stream.

Unlike control inputs of typical protective relays, the relay-to-relaydirect communication system disclosed herein includes communication linkmonitoring capability via detection of corrupted serial messages whenthey occur. That is, when a corrupted serial message is received by thereceive module 44, it may be concluded by the receive module that thecorrupted serial message is the result of faulty operation ordegradation of the communication link 34 and/or associated transmissionequipment. Suitable alarming may be utilized to notify the user of thecondition where the communication link 34 and/or associated equipmentremains faulty for a predetermined duration.

The relay-to-relay direct communication system disclosed herein alsoincludes communication link monitoring via detection of missing serialmessages. Because, the serial messages 67 are transmitted via thecommunication link 34 at pre-determined periodic intervals, or at apredictable rate, it can be concluded by the receive module that themissing serial message(s) 67 is/(are) the result of faulty operation ordegradation of the communication link 34 and/or associated transmissionequipment. For example, if the transmit module 41 is transmitting 250serial messages every second (a rate of one message every 4milliseconds), and the receive module 44 does not receive a serialmessage in an 8 millisecond period, a problem with the communicationlink and/or associated equipment may be concluded. In both-instances,the DOK flag 94 indicates the problem with the communication link 34and/or associated equipment, and the received analog values and/orvirtual terminal data is not utilized by the receiving relay (see, FIG.3).

The relay-to-relay direct communication system disclosed herein furtherincludes an ability to determine communication link availability, orchannel availability, defined as that portion of time the communicationlink 34 and/or associated equipment is capable of properly deliveringuncorrupted serial messages 67. Communication link availability may becalculated by dividing the aggregate number of all of the receiveduncorrupted serial messages by the total expected serial messages in arecording period. For example, for a recording period of 24 hours, at250 serial messages per second the transmitting module 41 transmits21,600,000 messages and the receive module 44 receives 21,590,000 serialmessages 67 because 9000 of the serial messages were corrupted and 1000of the serial messages were missing. The channel availability wouldtherefore be 21,590,000/21,600,000=99.9537%. Suitable alarming may beutilized to notify the user when the channel availability falls below apredetermined threshold.

As will be appreciated by one skilled in the art, variations ofavailability calculations are possible such as, for example, countingreceived frames 80 to determine availability of the digitized analogvalues and/or virtual terminal data. For example, because 18 receivedframes are needed to reconstruct an 18-bit digitized analog value,receipt of only 17 of the 18 frames would indicate an analog valueavailability of 94.44%.

Accordingly, the relay-to-relay direct-communication system disclosedherein is adapted to (1) directly communicate output status indicationbits which represent the result of protection functions by one of therelays, (2) directly communicate selected analog values representing oneor more functions of the relay, (3) directly communicate virtualterminal data provided by a user to one of the relays via the otherrelay, (4) monitor the communication link between the two relays, (5)determine communication link availability and (6) provide timesynchronization. The analog values and the virtual terminal data areprocessed in serial fashion in successive messages on channels not usedby the output status indication bits. The time synchronization data isprocessed in serial fashion in successive frames (18 messages) of data.

As noted above, the number of and assignment of data channels for theoutput status indication bits and the additional data (analog values andvirtual terminal data) can be pre-selected by an operator or can bedynamically selected during relay operation. The additional data mayinclude analog values only, virtual terminal data only or a combinationof analog values and virtual terminal data. The synchronization channelis dedicated for purposes of synchronizing the additional data, totransmit/receive additional virtual terminal data, time information andcalendar (date) information. This results in the channel capability ofthe basic transmission arrangement disclosed in the '750 patent beingused to its maximum extent, while providing the benefits of the existingfast and highly secure transmission of output status indication bits.

FIG. 4 illustrates a power protection system 400 utilizing a primary 410and a backup 420 protection device to oversee the operation of a circuitbreaker 430. As illustrated, both the primary device 410 and the backupdevice 420 are identical. The circuit breaker provides a breaker statussignal 434,436 to both the primary 410 and backup 420 devices. Thebreaker status signal 434,436 indicates whether the breaker is open orclosed, and is used by both the primary device 410 and the backup device420 to determine whether or not to open the circuit breaker on detectionof a fault.

The primary device 410 and the backup device 420 also provideovercurrent indications 444,446 to an alarm grid 440. Further, thebreaker provides a breaker gas pressure alarm signal 438 to the backupdevice 420. As explained later, the backup device transmits this alarmcondition over a link 415 to the primary device 410. The primary device410 processes the transmission and outputs a breaker gas pressure alarm448 to the alarm grid 440.

The primary device 410 is also connected to a communications network450. An operator may use a computer 460 connected to the same network450 to send commands to the primary device 410. The operator may alsodirect commands to the backup device 420 through the primary device 410,which is coupled to the backup device by link 415.

FIG. 5 is a block diagram of a device-to-device direct communicationsystem 500 within the power system 400, constructed according to anembodiment of the invention. FIG. 5 is largely analogous to FIG. 2,discussed earlier. However, FIG. 5 utilizes sixteen data channels, andtheir specific use is described below. The first eight data channels531-538 are used as “virtual output bits” for the primary device. Thevirtual output bits 511-518 denoted VOB₁-VOB₈ are transferred into thefirst eight data channels 531-538. The primary protective device 504transmits the status of the virtual output channels to the backupprotective device 556 which operates output contacts in accordance withthe virtual output channels, as explained later.

The next six data channels 519-524, denoted IB₁-IB₆ (input bit) arevirtual input channels. The primary protective device 504 collects thestatus of its input contacts 508 and places the collected status intothe input bits 519-524. Those bits are then transmitted to the backupprotective device 556, which maintains corresponding virtual input bits,and may use the virtual input bits in its internal calculations.

The final two data channels 525-526, denoted CMD1-CMD2 are commandchannels. Using these channels, the primary protective device 504 mayissue commands to the backup device 556. The commands may be relayedthrough the primary protective device 504 from an operator asillustrated in FIG. 4. The commands may also be sourced from theoperation of the primary device 504. For example, an external operatorcould alter the cold load pickup setting both the primary protectivedevice 504 and backup protective device 556 using the CMD data channels525-526.

When a frame is ready to transmit, the processor encodes at 550 the datausing any one of a number of suitable techniques. The data is thenpassed to a UART 552, where it is transmitted by a link 555 to thebackup protection device 556. The backup protection device 556 thenretrieves the data from a UART 579 and decodes at 580 the data intosixteen parallel received bits 561-576. The received bits 561-576 areseparated into OB₁₋₈ (output bits 1-8) 581-588, VIB₁₋₆ (virtual inputbits 1-6) 589-594, and CMD₁₋₂ (command bits 1-2) 595-596. The backupprotection device adjusts its output contacts (not shown) to conform tothe received output bits. It also updates its internal operations withthe virtual input bits, and executes any commands required by thecommand bits.

FIG. 6 is an exemplary received frame 600 of the device-to-device directcommunication system 500, according to an embodiment of the invention.As illustrated, the received frame includes sixteen bits. Of these,eight are output bits 620. The processor 660 reconfigures the outputcontacts 651-658 to match the state of the output bits 620. The receivedframe also includes six virtual input bits 616, which correspond toinputs of the primary protection device 504. The processor 660 adjustsits internal memory and operating state based on the virtual input bits630. Finally, the received frame includes two command channels 640.These channels may encompass messages that are many bits long, and willneed to be assembled frame by frame before they can be executed. Oncethe command messages are assembled, they are executed by the commandprocessor 640, which adjusts the internal state of processor 660 andoutput contacts 650.

The virtual input bits 616 can be used to convey the status of an inputcontact from one device to the other device. For instance, one devicemay monitor signals, such as a circuit breaker-in service signal, acircuit breaker test mode signal, or a circuit breaker manual closeindication signal. The monitored signals may then be transformed intodigital bits and transferred to the other device, where they are usedinternally in the second devices calculations. Other signals which maybe monitored using virtual input bits are cold load pickup on/off, orthe status of a second circuit breaker.

Each virtual output bit may be based on a single setting within theprimary protection device, or a combination of settings within theprimary protection device. The table below illustrates some common powerprotection settings:

Setting Description 50PH Phase Instantaneous Definite-Time OvercurrentElements 50N Residual Ground Instantaneous Definite-Time OvercurrentElements E50Q Negative-Sequence Instantaneous Definite-Time OvercurrentElements E51S Selectable Operating Quantity Inverse Time OvercurrentElement EV/D1 Manual Close Command for Circuit Breaker D1 EV/D2 ManualClose Command for Circuit Breaker D2 43OP Reclosing Control ActivationParameter 43PR 51PR Detector Activation Parameter

Virtual output bits may also be used so that one device; i.e.; theprimary device; may control output contacts on another device; i.e.; thebackup device. Some virtual output bit functions can be groundovercurrent on/off indication, remote on/off indication, andauto-reclosing of the second circuit breaker.

So, for instance, using the disclosed invention, a virtual output bitcould be set in the primary based on a negative-sequence instantaneousdefinite-time overcurrent element (E50Q), or it could be based on anegative sequence instantaneous definite-time overcurrent element and aphase instantaneous definite-time overcurrent element (50PH).

Note that the invention described herein utilizes a digital processor.As the algorithms described do not require any particular processingcharacteristics, any type of processor will suffice. For instance,microprocessors, microcontrollers, digital signal processors, fieldprogrammable gate arrays, application specific integrated circuits(ASIC) and other devices capable of digital computations are acceptablewhere the term processor is used.

In addition, the term intelligent electronic device is used. Anintelligent electronic device is defined, for terms of this application,as a power protection device (i.e.; non-power protection devices such asgeneral computers are not intended) including a processor for decisionmaking. Examples of intelligent electronic devices are relays of varioustypes and recloser controls.

The foregoing description of the invention has been presented forpurposes of illustration and description, and is not intended to beexhaustive or to limit the invention to the precise form disclosed. Thedescription was selected to best explain the principles of the inventionand practical application of these principles to enable others skilledin the art to best utilize the invention in various embodiments andvarious modifications as are suited to the particular use contemplated.It is intended that the scope of the invention not be limited by thespecification, but be defined by the claims set forth below.

1. A device-to-device direct communication system in a power systemcomprising: i) a first intelligent electronic device having a firstprocessor and a transmit module coupled to a communication link and theprocessor, the processor providing a plurality of data channels andforming channel data including at least one virtual output; and ii) asecond intelligent electronic device coupled to said first intelligentelectronic device with the communication link, the second processor, anda receive module coupled to the communication link, the second processoraccepting the plurality of data channels and said channel data includingthe at least one virtual output to control said output of the secondintelligent electronic device.
 2. The device-to-device directcommunication system of claim 1, wherein the second intelligentelectronic device is identical to the first intelligent electronicdevice.
 3. The device-to-device direct communication system of claim 1,wherein the first intelligent electronic device and the secondintelligent electronic device are configured in a primary-backup scheme.4. A device-to-device direct communication system in a power systemcomprising: i) a first intelligent electronic device having a firstprocessor and a receive module coupled to a communication link and theprocessor, the processor accepting a plurality of data channels from thecommunication link including at least one virtual input, the processorchanging its internal state based on the at least one virtual input; andii) a second intelligent electronic device coupled to said intelligentelectronic device with the communication link, said second intelligentelectronic device having at least one input, a second processor coupledto the at least one input, and a transmit module coupled to thecommunication link and the second processor, said second processorproviding said plurality of data channels and forming channel dataincluding said virtual input corresponding to said input, andtransmitting said channel data to said first intelligent electronicdevice with the transmit module.
 5. The device-to-device directcommunication system of claim 4, wherein the second intelligentelectronic device is identical to the first intelligent electronicdevice.
 6. The device-to-device direct communication system of claim 4,wherein said first intelligent electronic device and said secondintelligent electronic device are configured in a primary-backup scheme.7. The device-to-device direct communication system of claim 4, whereinsaid first intelligent electronic device further comprises a tripoutput, and the trip output is based on the at least one virtual input.8. A device-to-device direct communication system in a power systemcomprising: i) a first intelligent electronic device having a commandinput, a first processor, and a transmit module coupled to acommunication link, said first processor providing a plurality of datachannels and forming channel data including at least one virtual commandformed from the command input; and ii) a second intelligent electronicdevice coupled to said first intelligent electronic device by saidcommunication link, said second intelligent electronic device having areceive module and a second processor, said second processor acceptingsaid plurality of data channels and said channel data including saidvirtual command and executing said virtual command.
 9. Thedevice-to-device direct communication system of claim 8, wherein saidsecond power protection device further comprises at least one output,and wherein said second processor executes said command and in responsethereto alters said output.
 10. A method for a first intelligentelectronic device to control at least one output contact of a secondintelligent electronic device comprising the steps of: i) forming aplurality of data channels including at least one virtual output bit onthe first intelligent electronic device; ii) transmitting the pluralityof data channels to the second intelligent electronic device; and iii)adjusting the at least one output contact of the second intelligentelectronic device based on the at least one virtual output bit.
 11. Amethod for a first intelligent electronic device to monitor at least oneinput contact of a second intelligent electronic device comprising thesteps of: i) forming at least one virtual input bit corresponding to theat least one input contact of the second intelligent electronic device;ii) forming a plurality of data channels including the at least oneinput contact on the second intelligent electronic device; iii)transmitting the plurality of data channels to the first intelligentelectronic device; and iv) adjusting the internal state of the firstintelligent electronic device based on the at least one virtual inputbit.
 12. A method for a first intelligent electronic device to forwardcommands to a second intelligent electronic device comprising the stepsof: i) receiving a command at the first intelligent electronic device;ii) forming at least one command channel based on the command; iii)forming a plurality of data channels including the at least one commandchannel; iv) transmitting the plurality of data channels to the secondintelligent electronic device; and v) executing the command on thesecond intelligent electronic device.